This is where an opinionated linter comes in handy. Ensures people gradually move to the “better” version while not breaking backwards compatibility.

It does suck for beginners who end up having to know about all variations until their usage drops off.

The linter is a big deal, actually. I've worked with Python off and on during the past few decades; I just recently moved onto a project that uses Python with a bunch of linters and autoformatters enabled. I was used to writing my strings ('foo %s % bar), and the precommit linter told me to write f'foo %{bar}'. Easy enough!